[Nut-upsuser] Fwd: Cyberpower usbhid-ups wrong battery voltage

[Arjen de Korte]

> Because HID descriptors allow units of length, mass, time, temperature,
> CURRENT (A), luminous intensity but doesn't allow the VOLTAGE (V)
> (whoever invented this HID standard should be more grateful with
> units to choose from)

Please read the HID PDC specification first, lsusb is wrong here. To
summarize, NUT is doing the correct calculations but the UPS is reporting
incorrect values. Note that the people that wrote the HID parser for NUT
(MGE UPS systems) also were involved in writing the HID PDC specification
so they know what they are talking about.

> So the manufacturer's only choice was an undimensioned
> unit (it is supposed to be linear and SI stanadard compliant meaning
> nothing else but VOLT).

No. See above. CyberPower got it right with the nominal battery voltage,
but they messed up terribly with the readings for the battery voltage. In
all likelyhood, they forgot to set the PhyMin and PhyMax values. If you
set them to 9.8 and 14.4 respectively (which would be reasonable values
for a 12V PbAc battery), you'd get a physical value of 13.6 for the
logical value 211 that is read from the UPS.

> But it isn't. we could properly scale it to volts anyway using some
> config files but now we need to mach vendor/product id and go thru
> the hassle of per-vendor-device conversion coefficients

Yes.

Best regards, Arjen